It said US Vice President Joe Biden, the administration's prime contact with President Viktor Yanukovych in recent days, spoke to the Ukrainian leader by telephone yesterday and made clear the US is prepared to sanction those officials responsible for the violence.

Military action by the US is not among the options being considered, deputy spokesman Josh Earnest said.

"The options available to the president are being considered with some urgency," he told reporters. He said sanctions were the only measure under active consideration.

Navy Rear Admiral John Kirby, a Pentagon spokesman, told reporters that defence secretary Chuck Hagel had tried to reach the Ukrainian defence ministry to discuss the violence, but "they have been unresponsive to our requests".

Mr Kirby said the lack of responsiveness was unprecedented.

Mr Earnest said the Ukrainian government has the primary responsibility for keeping the peace but that the Ukrainian people must also respect their right to peaceful protest.

He said "having those rights trampled" is a source of some concern to the US, and again called on the government and the opposition to negotiate a political solution to restore order.

"Basic human rights that we hold so dear in this country are not being respected in that country," He said.